The invention relates to a system for marking moving objects by laser beams, comprising a source emitting laser beams along a path.
With increasing frequency, the packages or the products themselves have to be marked with data indicating a date, a lot number, an expiry date or other detail which is only known as from a particular moment in time, such as when the product has been packaged or when the product itself was prepared. This requirement relating to the time of marking prevents its prior inclusion in the label print, in the package print or, for example, in the mould for final preparation of the product.
Furthermore, the production, packaging or the like frequently proceeds at a very high rate whereby marking with conventional means would involve a very considerable loss of time.
As a result of the above circumstances, recourse has already been had to laser beams for the said marking operation, on the basis that said laser beams may produce a large amount of energy at the point of impingement. Nevertheless, the generally known systems are based on the insertion of a mask between the laser beam source and the area to be marked. A mask is a device which only allows the beams to pass through interstices defining the signs to be marked. Nevertheless, these masks provide images which are not variable in time and to be able to produce different images, it is necessary to have a plurality of masks available, the appropriate disposal of which is controlled by a stepper motor, with a long time of passage from one letter to another of about 200 milliseconds. The time of passage between letters is understood to be the time which has to elapse between one alphanumeric character and the next one for the process to be correct.
On the other hand, there is known one property of the germanium crystal making it capable of modifying its refractive index depending on the frequency of a received sound signal. To achieve these modifications, there is adapted a transducer of a highly conductive material which performs the function of adapting the germanium crystal to a sound signal, i.e., the speed of sound (5,500 m/s) within the crystal.
On application of this property is know with respect to the configuration of a laser generator. This configuration is basically as follows:
A constant wavelength photon generator means, such as a low pressure plasma tube with a gas mixture (CO.sub.2, N.sub.2, He), is taken and an electric field is created therein, producing a photon beam. This photon beam is guided in a cavity formed by two mirrors, one partly reflective and the other 100% reflective.
When the accumulated light energy is sufficiently high, a laser emission occurs through the partly reflective mirror.
To produce a pulsed laser beam, there is inserted within the laser cavity in the direction of the photon beam a germanium crystal with a transducer which when it is excited with a radio frequency signal causes a deviation of the photon beam path, interrupting the laser emission.
When the radio frequency signal is interrupted, the photon beam path is restored, producing a laser emission again. It should be noted that during the time the beam is interrupted there is a considerable increase of energy within the cavity, producing a high energy laser pulse when the emission is restored.